Automatic stabilizer for watercraft



April 23, 1968 J. PLUM 3,379,158

AUTOMATIC STABILIZER FOR WATERCRAFT Original Filed Feb. 25, 1965 Sheets-Sheet l TOTA L DR AG FRICTIONAL ,2 DRAG INDUCED DRAG (Wtuna O I l I l I l l '0 2o 40 5O 7O TRIM ANGLE, d

INVENTOR. JOHN PLUM April 2 3, 1968 J. PLUM 3,37

AUTOMATIC STABILIZER FOR WATERCRAFT Original Filed Feb. 25, 1965 5 Sheets-Sheet 2 FIQZ.

INVENTOR. JOHN PLUM BY Warn ApriH 23 1 968 J. PLUM 3,379,158

AUTOMATIC STABILIZER FOR WATERCRAFT Original Filed Feb. 25, 1965 5 Sheets-Sheet 3 FIG. 4. v I MENTOR JOHN PL UM April 23, 1968 .1. PLUM 3,379,158

AUTOMATIC STABILIZER FOR WATERCRAFT Original Filed Feb. 25, 1965 5 Sheets-Sheet 4 v INVENTOR. 60 JOHN PL UM April 23, 1968 J. PLUM 3,379,158

AUTOMATIC STABILIZER FOR WATERCRAFT Original Filed Feb. 25, 1965 5 Sheets-Sheet 5 INVENTOR.

JOH/V PLUM Unied States Patent ABSTRACT (BE THE DIStCLOSURE An apparatus adapted to stabilize stepped planing hulls. The apparatus may be controlled to provide a negative trim angle to pull down the stern portion of the vehicle and a positive trim angle to lift the stern portion of the vehicle.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present application is a divisional application of applicants co-pending application Ser. No. 435,383, filed Feb. 25, 1965.

This invention relates to a stabilizing arrangement for stepped planing hulls and more particularly to a stabilizing arrangement which is an improvement on the device shown, described, and claimed in U.S. Patent No. 1,618,- 995; US. Patent No. 1,779,075 and U.S. Patent N0. 1,875,135.

It is known to workers in this art that the stepped planing hull has great potential value if a practical solution can be found to eliminate some of its faults. Principal among these faults is the fact that the trim angle of the boat is affected much more by the magnitude and location of an added load than in the case of the stepless hull.

These problems will be readily understood when it is realized that the conventional stepped hull is supported by two planing surfaces traveling in tandem so that the afterbody is supported by water which has already been deflected by the forward planing surface.

If the forward planing surface is carrying a load, it will carve a groove in the water into which the afterbody will settle, thereby increasing the trim angle of the forebody. This increase will, in turn, increase the depth of the groove into which the afterbody will further settle. It is a vicious circle or chain reaction which greatly affects not only the trim angle of the stepped hull but also its pitching motions, which may be amplified into violent porpoising at high speed.

The amplifying effect of the downwash from the forward area can be curtailed by reducing the load on the forward planing surface to a minimum because, with a negligible load forward, there will be a negligible deflection of the water and, therefore, no amplifying effect. But without a forward load (i.e., a mass on the wave impact area), the pitching motions of the bow will be excessive and, if the waves are permitted to pass the forebody without being dispersed, the acceleration or pounding of the hulls afterbody will be violent and the bow portion of the hull will drop faster than a freely falling body. This phenomenon Was clearly demonstrated during the last war when crew members in the forward sections of P. T. boats were seen standing in midair. This is explained by the fact that an upward acceleration of the stern will make the hull pivot about its center of gravity a moment after it has pivoted about its transom. This will accelerate the downward motion of the bow, and when the downward velocity is arrested by an oncoming wave, the maximum hull acceleration, i.e., pounding, is produced.

Before proceeding further, it is to be understood that the statements made herein apply not only to vessels or boats having stepped planing hulls but also equally as well to stepped flying boat hulls.

In the case of the flying boat such extreme accelerations are eliminated, and control of trim is obtained by lifting the afterbody clear of the water by the air-foil stabilizers and elevators when sufficient air speed is attained. In fact, the functioning of the flying boat demonstrates adequately the advantages that can be obtained by the stepped hull if its afterbody can be lifted clear of the water and stabilized by a surfboard at the stern. It should be realized that when the afterbody of the stepped hull is lifted clear of the water in this manner, the forward step is, in effect, the transom of the hull proper, and the afterbody becomes a stern extension by which the surfboard is towed.

In contrast to the towline by which a surfboard is usually towed without drag on the wave (or upwash) tha follows a speed boat, the stern extension is a rigid part of the hull. To eliminate the maximum pounding and/or the amplifying effect of the downwash, the surfboard (or the stabilizer) must, therefore, be free to follow the irregularities in the water surface on which it is riding without enforcing these on the rigid stern extension. According to the present invention, the stabilizer supports the stern extension through a cushion of compressed air, the pressure of which (controlled by the pilot) decides the height at which the afterbody is lifted above the water surface. This in turn decides the magnitude of the hulls trim angle.

The magnitude of the trim angle is an important factor involved in the wavemaking resistance (called the induced drag) of planing hulls. In FIG. 1 is shown a typical empirical resistance curve for a planing hull at the representative speed of 50 knots.

It is seen that the optimum trim angle producing the smallest drag is 5 /2 degrees even though the induced drag is enormously high. The induced drag is found by multiplying the weight of the hull by the tangent of the trim angle so that in the case of a 50-ton hull some 10,000 pounds of propeller thrust are required to overcome the induced drag. Nevertheless, a large trim angle, which reduces the wetted area of the hull (i.e., of the forebody), gives the maximum speed of the conventional stepless hull in smooth water. This proves that the frictional resistance is a drag-producing factor out of all proportion to the other factors, including the induced drag.

Accordingly, the wetted area of the hull bottom should be reduced to the smallest possible value. But the method (conceived 50 years ago) of reducing the wetted area of the forebody by increasing the trim angle is Obsolete compared with the method of eliminating all of the wetted area of the afterbody by reducing the trim angle. For instance, by reducing the latter from 6 degrees to 2 degrees at a speed of 50 knots, the 10,000 pounds of induced drag of SO-ton hull is reduced 68 percent.

Since the induced drag is a function of the hull weight and the trim angle, it becomes increasingly clear that the optimum trim angle of the planing surface should have the smallest possible value. This is especially important in the case of a craft designed for carrying heavy loads at high speeds. Such a quality has been found in the cambered planing surface which is described and claimed by me in U.S. Patent No. 1,618,955 issued March 1, 1927.

If the camber of a longitudinally concave planing surface starts with an angle of attack of zero degree, the downward acceleration of the water particles along the (3 camber will be gentle and uniform, which in turn will produce a reaction (or lift) of surprisingly high efiiciency. In fact, papers by Wagner (1932 and 1933); Tulin (1957); advocate the use of the cambered planing surface for reducing the drag, especially the wavemaking drag.

The frictional resistance of the cambered planing surface cannot be ignored. But if the area (or beam) of the latter is excessive for the load carried at the boats maximum speed, the angle of attack of the camber can, of course, be reduced to zero. In other words, if a trim controlled stepped hull with a cambered planing surface already gets into planing condition at 30 m.p.h.; with zero angle of attack its beam and wetted area will be far too large at 60 mph. Therefore, an additional load on such a hull will neither require an increase of trim angle nor a larger planing area. Hence, neither the induced drag nor the frictional resistance will be increased by an additional load at 60 mph.

It is obvious that cambered bottom lines cannot be used in stepless planing bulls without causing a nose-down attitude which will increase the wetted area of the forebody and the tendency to broach in following seas. However, the efiiciency of the camber when combined with control of trim has been confirmed in actual service by the stepped hulls of flying boats, such camber having been previously incorporated into the stepped hulls of flying boats by the US. Navy (1927). Further confirmation was provided by F. W. Horenburger, surveyor of the American Power Boat Association, who timed a 500-h.p., 40-ft. stabilized stepped hull with a camber-ed planing surface at 62.5 mph. Its maximum speed was attained with a ballast of 4000 pounds or a 33 percent increase of the hull weight. In this case the stabilizer carried about 15 percent of the load or some 2000 pounds while 14,000 pounds were carried by the forward planing surface.

Since hull accelerations (pounding) are inversely proportional to the mass at the wave impact area and directly proportional to the magnitude of the trim angle, the pres ent invention improves the speed and comfort of small craft. And since the present invention permits the pilot to reduce the trim in head seas and increase it in following seals, the invention is also a improvement in the safety of the small craft.

It is, therefore, an object of the present invention to provide a stabilizer for a stepped planing hull which may be controlled to have negative and positive trim angles and further to have hydrodynamic surfaces which are simple to manufacture and which are capable of providing lift action without causing directional forces.

The present invention when applied to flying boat stepped hull configurations enhances not only the takeoff mode of the aircraft but also enhances its landing mode. For example, during the takeoff mode, the increasing trim angle of the hull during acceleration is also enforced on the stabilizer which will travel submerged until its trim angle has become sufiiciently lift producing to enable it to break through the water surface and become a surf riding aquaplane. Once the stabilizer acts as an aquaplane, the drag induced on the afterbody of the aircraft is so greatly reduced that the airplane may easily take off with loads substantially greater than would be otherwise possible without the stabilizer. The further advantage accruing to the present invention is the fact that when the flying boat is initially moved in its takeoff mode, the stabilizer is at a negative trim angle. Therefore, upon movement of the aircraft, the stabilizer tends to pull down on the stern portion of the aircraft thereby forcing the aircraft into an initially positive trim angle and further counteracting the moments of the thrust of the propellers which would tend to cause the airplane to nose down.

During the landing mode of the flying boat, as the aircraft approaches and makes contact in its stern portion with the water, the stabilizer has a negative trim angle Cir tending to pull down the stern, slowing down the aircraft and preventing the aircraft from nosediving.

A principal object of the present invention is to provide a stabilizing arrangement enabling heavily loaded stepped flying boat hulls to acquire the optimum trim angle or lift-drag ratio during the time the flying boat is accelerated to higher speeds.

The foregoing object and advantages of the invention as other features of the invention will be better understood by reference to the following detailed description and accompanying drawings in which:

FIG. 1 (previously referred to) is a graph depicting drag characteristics of planing craft;

FIG. 2 is a view in modified longitudinal cross-section of the stern portion of a stepped planing hull provided with a stabilizer shown in its retracted position and control means therefor in accordance with the invention;

FIGS. 3 and 4 are views in modified longitudinal cross section of the stabilizer of FIG. 2 in its partially extended and fully extended positions respectively;

FIGS. 5, 6 and 7 are views of the stabilizer in various positions during its operation according to the invention;

FIGS. 8, 9, l0 and 11 are side views of a flying boat incorporating the stabilizer according to the present invention and showing the flying boat in relative positions with respect to the water during landing or takeoff.

The stabilizer according to the present invention is shown in FIG. 2 arranged in a recessed portion 9 below the stern portion of a boat hull 11 having a rudder 12. The recessed portion 9 has a longitudinal central recess 13, best seen in FIGS. 6 and 7, extending to the transom. The forward end of the recessed portion 9 terminates in a shallow step 15 defined by athwartships block 17. As a non-limiting example, the dept hot the step 15 may be about 2 inches in a boat approximately 30 feet long.

Transverse and longitudinal structural members 18 of the craft near the step 15 are arranged to define a generally cylindrical space 19 for housing a canted cylinder 20. The top of the space 19 is defined by a sturdy structural frame 21 rigidly attached to hull members. The sides of the space 19 are defined by members 23 secured at their tops to the hull members and member 21 and at their bottom to the hull. The members 21 and 23 provide a strong base so that a clamp (not shown) may be mounted on the member 21 to hold the cylinder rigidly in place.

The bottom of the opening 19 is sealed against sea water by an annular sealing element 25 of any suitable construction. The annular member 25 also serves as a radial support for an end fitting 31 having an axial bore 33 and fluidtightly secured to the bottom of the cylinder 20.

The axis of the canted cylinder 20 is indicated by numeral 35 and has its upper end substantially forward of its lower end. The upper end of the cylinder 20 is fluidtightly sealed by a head 37.

Located within the cylinder at its bottom just above the end fitting 31 is annular seal and roller bearing unit 38 of any suitable construction.

A double acting piston 39 is mounted within the cy1inder 20 and has on its upper surface a mounting element 41 for receiving a Wire 43. The wire 43 passes fiuidtightly through the head 37 and extends to an instrument panel on the craft for indicating the exact axial position of the piston 39 in the cylinder 20.

A hollow piston rod 49 is rotatably mounted at its upper end to the piston 39 by means of a ball bearing 50 of any suitable construction and arranged so that the rod 49 does not move axially relative to the piston 39. The piston rod 49 therefore moves axially with piston 39 but rotates independently thereof about the canted axis 35. The diameter of the piston rod 49 is such that the rod passes in close sliding relation with the inner race of the roller bearing in unit 38. The cylinder 20 is thus sealed at both ends.

A compression spring 51 is located between the wall of the cylinder and the piston rod 49 and has its upper end resting against the lower surface of the piston 39 and its lower end resting against the upper surface of the unit 38. The purpose of the spring 51 is to hold the piston in place when the stabilizer and its controlling means are not in actual operational use. The spring 51 also acts as a stop to prevent excessive downward movement of the piston.

The axial position of the piston 39 is controlled by means of high pressure air coupled to the cylinder 20 via an upper conduit 52 and a lower conduit 52a. The high pressure air may contain a small amount of oil entrained therewith to provide a good seal between piston 39 and cylinder 20.

Rigidly attached to the lower end of the piston rod 49 is a foot 53 made of sturdy material such as metal. As best seen in FIG. 5, the forward end of the foot has a bore 54 and a central longitudinal slot 54a extending a short distance aftwardly therefrom. A plurality of studs 54b pass transversely thru the slot 54a, foot 53, the lowermost of the studs passing thru a portion of the wall of rod 49, to securely hold the foot 53 rigid to the rod 49. Thus the entire foot 53 moves in unison with the piston rod 49 in rotation and translation.

At the aft end of the foot 53 is a transverse hinge defined by a pin 55. The stabilizer element 57, is connected at its aft end to the pin 55 by means of a block 59 carrying the pin 55. Studs 68 secure the block 59 to the stabilizer and hold the block in place. The exact shape of the surfaces of stabilizer 57 will be described in more detail in conjunction with FIGS. 5 thru 7.

The upper portion of the stabilizer 57 has a longitudinal central recess 61 into which, as shown in FIGS. 3 and 4, the foot 53 is pushed when the stabilizer 57 is lowered. Secured to the forward end of the recess 61 of the stabilizer is a eyelet 63. The eyelet 63 is located approximately on the axis 35. A depending eyelet 65 is attached to the upper interior end of the piston rod 49. A tension spring 67 has its upper end connected to the eyelet 65 and its lower end connected to the eyelet 63, so that the spring 67 tends to draw the forward end of stabilizer 57 toward the foot 53.

Just aft of the step 15 is provided a roller element 69 having a longitudinal axis of rotation. The stabilizer 57 has a faired leading edge 71 the upper surface of which is held in intimate contact with the bottom surface of the roller 69 by the action of the tension spring 67 thereby providing a pivot for the stabilizer during the initial stages of downward motion of the stabilizer.

A limit stop 73 mounted on. each side of the foot 53 is rotatably mounted on a transverse pin 74. The pins 74 are mounted on each side of the recess 61 of the stabilizer. The foot 53 has a pin 75 extending tranversely thru the foot 53. The limit stop 73 has an elongated central slot 77 receiving the pin 75 so that the movements of the stabilizer 57 away from the foot 53 are limited.

As previously mentioned, stabilizer 57, shown in a drawn up (retracted) position in FIG. 2 has in that position an attack angle that is negative with respect to the forebody.

The magnitude of the trim angle or positive attack angle of the stabilizer is dependent upon the attack angle of the bottom surface of the foot 53 as installed. Any suitable means may be employed for adjusting the attack angle of the foot during or after the original installation of the equipment. When, as shown in FIG. 3, the foot is initially lowered by applying air to the cylinder via conduit 52, the stabilizer 57 rotates about the pin 55 and pivots with some aftward sliding motion at its leading edge 71 so that the entire bottom surface of the foot 53 is in intimate contact with the floor of the recess 61. Consequently the stabilizer is advantageously supported along nearly its entire length by the foot 53 when the foot is lowered to and below its position shown in FIG. 3. The

stabilizer may be lowered to any position until the piston is stopped by spring 51.

When the foot 53 is lowered still further, it loses contact at its leading edge with the roller 69. The stabilizer has a positive trim angle and is completely free to move in modes following local water disturbances. The FIG. 4 position of the stabilizer is the desired position for use in the planing mode of the craft. The movement of water in relation to the stabilizer 57 is exemplarily indicated in FIG. 4. The motion of the stabilizer in its free posi tion (FIG. 4) can be understood by realizing that the stabilizer when planing always tends to remain oriented in a horizontal plane, even when the craft is heeling. Recall that the piston rod 49 may rotate about forwardly canted axis 35. With such a canted axis, when the stabilizer 57 has positive trim angles, rotation of the stabilizer about the canted axis 35 causes one aft corner of the stabilizer to be elevated while the other aft corner is lowered. When the craft heels, the axis 35 of course, moves with the craft and the stabilizer initially heels with the craft. Subsequently, the stabilizer rotates about axis 35. The rotation of the stabilizer is caused by greater drag acting on the low side of the stabilizer. This rotation of the stabilizer about the canted axis 35 causes the initially low side of the stabilizer to return to same, or another horizontal plane with its longitudinal axis different from that of the heeled craft. Thus the stabilizer remains essentially horizontal when the craft is heeled.

As seen in FIGS. 5, 6 and 7, the stabilizer 57 is formed of two continuously curved surfaces symmetrical about the longitudinal axis of the stabilizer and meeting each other at the leading edge and sides. The curved surfaces may be portions of right circular cylinders, or any other cylindrical or continuously curved shape. As an example, but not a limitation, the stabilizer as shown has upper and lower curved surfaces 81 and 83, the curvature of the lower surface being greater than that of the upper. The lower surface is transversely convex with respect to the water, and in all its transverse cross sections the stabilizer has essentially a crescent shape. In longitudinal cross section, the stabilizer has a wedge shape with a f-aired leading edge (FIGS. 2 thru 4), and in plan view (FIG. 5) the stabilizer has a generally semi-circular shape. A sturdy crescent-shaped strength member 85 supports the aft ends of the surfaces 81 and 83. The surfaces may be made of any suitable material, e.g. metal or Fiberglas, or the like, and may be joined at their edges and at strength member 85 in any suitable manner, as by welding, bonding, etc. Preferably the stabilizer may be formed to have a unitary integral structure by any suitable method, such as by injection molding, lay-up, casting, etc.

Near the outer edge of the deadrise beneath each side of the stern is located a block 87 made of any suitable slippery material such as nylon, Teflon, Kel-F or the like. When the stabilizer 57 is to be drawn up (retracted) from its positions shown in FIG. 4 and FIG. 3 to that shown in FIG. 2 (and FIG. 6), the blocks 85 serve to center the stabilizer. This action is shown in FIG. 7. The upper surface 81 may have one side in a higher position than the other relative to craft 11 due to local water conditions, or due to heeling. As exemplarily shown in FIG. 7 the night hand side of the stabilizer is higher. As the stabilizer is drawn up (by injecting high pressure air into the cylinder via lower conduit 52a), the higher right hand side eventually comes into intimate contact with a block 85. As the stabilizer moves upward the surface 81 slides essentially laterally along past the block 87, the block 87 having a camming action. When the stabilizer is fully retracted (FIG. 6), the longitudinal axis of the stabilizer parallels that of the craft 11.

In FIGS. 8-11, the invention is shown applied to a flying boat 91 having a midships step 93 in the hull. The stabilizer 57 is shown mounted on the afterbody near the tail end of the hull and is depicted in exaggerated positions for purposes of descriptive clarity.

During takeoff, power is applied to the flying boat which is at rest as shown in FIG. 8. Ordinarily a sudden increase in power would tend to cause the flying boat to nose dive. However, according to the invention, the stabilizer is given a suitable negative trim angle so that when power is initially applied, and the flying boat begins to move, the stabilizer tends to pull the a'fterbody down. The lowerng of the afterbody immediately establishes a positive trim angle for the flying boat, reducing total drag. As the flying boat is increased, say to about 10 kts, as shown in FIG. 9, the stabilizer 57 is given a suitable positive trim angle, resulting in lifting the afterbody to prevent excessive hull trim angle. Minimizing the trim angle of the hull reduces induced drag and enables greater takeoff loads and shorter takeoff runs that would be possible with large hull trim angles during takeoff. As can be seen in FIG. 9, the hull planes on the step 93 and stabilizer 57 in tandem therewith. The advantageous use of the stabilizer thus results in a minimum of wetted area and a minimum trim angle, thus reducing total drag.

As the flying boat speed is further increased, the airfoils in the tail eventually lift the afteroody from the water, as shown in FIG. 10. The stabilizer may then be retracted as shown. The amount of lift necessary to pull the afterbody from the water is reduced according to the invention because of less wetted area in the afterbody and because of the aiding stern-lifting action of the stabilizer. The flying boat is then planing at high speed on its forebody and is ready for liftoff.

During landing the stabilizer 57 is maintained in its retracted, negative trim angle position so that, as shown in FIG. 11, as the flying boat touches down, a moment before the forebody touches the water surface, the stabilizer will become submerged at a negative trim angle (shown somewhat exaggerated in FIG. 11). The effect of the action of the stabilizer is to anchor the afterbody to the water surface while decelerating the hull with its drag.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A stabilizing apparatus for a marine vehicle comprising:

a stabilizing element located beneath the stern portion of the vehicle;

a foot support means pivotably attached to the upper rearward portion of said stabilizing element for providing vertical swinging motion to said stabilizing element; reciprocating means, securably attached to the forward portion of said foot support and securably attached to the under portion of the vehicle, for providing vertical reciprocal movement to said stabilizing element; whereby said stabilizing element is provided with vertical reciprocal movement, vertical swingable movement about a longitudinal axis and vertical swing able movement about a transverse axis. 2. A stabilizing apparatus for a marine vehicle, as defined in claim 1, wherein:

said stabilizing element has a lower cylindrical surface and an upper cylindrical surface, the axes of said cylindrical surfaces generally aligned with the longitudinal axis of the marine vehicle. 3. A stabilizing apparatus for a marine vehicle, as defined in claim 2, wherein:

said cylindrical surfaces have different radii of curvature. 4. A stabilizing apparatus for a marine vehicle, as defined in claim 3 wherein:

said axis of said upper cylindrical surface is inclined relative to said axis of said lower cylindrical surface to define a greater thickness at the rear of said stabilizing element than the thickness at the front of said element;

whereby said lower surface provides a positive trim angle to lift the stern portion of the vehicle and said upper surface provides a negative trim angle to lower the stern portion of the vehicle.

5. A stabilizing apparatus for a marine vehicle, as

' defined in claim 4, further comprising:

References Cited FOREIGN PATENTS 10/ 1922 Germany.

4/1958 Italy.

ANDREW H. FARRELL, Primary Examiner. 

